1. Field of Invention
This invention relates to a composite structures and more particularly, the to composite structures which are especially adapted for forming high strength panels suitable for use in applications requiring a capability to withstand point compression loading without deformation.
2. Description of the Related Art
Composite panels are commonly used in various applications such as cargo containers, vehicles, and boats. In the past, boat transoms have been developed using a variety of different technologies. One prior art technique for forming transoms uses plywood as the core of a sandwich laminate. The plywood acts to augment the structural properties of the fabric layer skins of the transom. Advantageously, plywood provides a low-cost means for strengthening the transom. Additionally, plywood has excellent compressive strength for through bolting and outboard motor clamps. One significant drawback to working with plywood, however, is that it tends to decay significantly, often within five to seven years.
Another prior art technique for forming transoms uses a high-density structural foam core rather than a plywood core. The high-density structural foam is commonly formed from cross-linked PVC or very high-density urethane. Transoms having high-density structural foam cores commonly maintain their structural integrity for up to ten years. High-density structural foam is considerably more expensive than plywood, however, and is not cost effective to use throughout the entire transom. The high-density foam resists compression resulting from point loading of the transom panel associated with motor mounting bolts. It should be noted that even high density foam will be subject to creep or relaxation over time and in some instances over temperature variations. Yet another prior art technique for forming a transom includes a composite of both high and lower density structural foams. In this technique, high-density structural foam is provided only in areas, which will support through bolts and/or outboard motor clamps, and low-density structural foam is provided in the remaining portions of the transom core. There are several drawbacks to this technique. One drawback is that during transom manufacturing with structural foam, the structural foam is typically attached to a mold using only a few large C-clamps. This attachment structure is not acceptable for a composite structure formed from numerous pieces of foam because each piece of foam would not be attached to the mold. An additional drawback is that properly combining the high and low-density structural foams requires a high degree of precision, and is therefore costly. Besides cost, the techniques previously discussed are poorly designed for manufacturability and production.
U.S. Pat. No. 5,429,066 to Lewit et al. involves manufacturing a composite structure that has a reinforced fabric layer. A non-woven fabric layer, such as a mat fiber layer, is attached to the reinforcing fabric layer. A structural foam is attached to the non-woven fabric layer on the side of the non-woven fabric layer opposite the reinforcing fabric by filling the interstices of the non-woven fabric layer. However, the Lewit. ""066 structure suffers from the inability to resist point compression loads such as those associated with outboard motor mounting bolts.
U.S. Pat. No. 5,908,591 to Lewit et al. involves manufacturing a composite structure having a structure similar to Lewit ""066. Significantly, however, the Lewit ""591 composite structure does not make use of a second reinforcing fabric layer. Instead, penetration of the structural foam is controlled so as to leave an outer portion of the fabric layer of the cured composite structure substantially free of cured resin.
Thus, a need exists for a composite structure that is easily manufacturable and that is able to resist point compression loads such as those associated with outboard motor mounting bolts.
A composite panel and a method for making same is disclosed which is formed of a foam core and is able to resist compression caused by point compressive loads. In a first aspect of the present invention the method preferably comprises the steps of providing a panel having elongated channels formed therein which are positioned along areas of anticipated point compression loading. The panel is preferably constructed by attaching a reinforcing fabric layer to a non-woven fabric layer forming an outside layer. Additionally, the panel has foam core within the outside layer. The method further comprises providing structural foam channel inserts having an outer fabric layer, wherein the channel inserts have a cross section that matches the cross-sectional profile of each of the elongated channels of the panel. Resin is then applied to the outside layer of the panel and outer fabric layer of the channel inserts such the channel inserts are positioned within the channels of the panel. The resin is then allowed to cure forming a composite structure.
In a second aspect of the present invention, a method of forming high strength panels comprises the steps of providing a panel by attaching a reinforcing fabric layer to a non-woven fabric layer forming an outside layer, wherein the outside layer forms opposing panel surfaces. A plurality of point compressive load bearing members are then arranged between the opposing panel surfaces along areas of anticipated point compression loading, wherein the plurality of point compressive load bearing members forms elongated channels which are applied transversely to opposing surfaces of the panel. The panel and the plurality of point compressive load bearing members are placed within a mold and the plurality of point compressive load bearing members are then secured in place within the panel by injecting the mold with foam providing a foam core to the panel.
In a final aspect of the present invention, a composite structure comprises a panel having elongated channels formed therein which are positioned along areas of anticipated point compression loading, wherein the panel is arranged and constructed by attaching a reinforcing fabric layer to a non-woven fabric layer forming an outside layer. The composite structure further comprises a plurality of structural foam channel inserts, each insert formed from attaching a reinforcing fabric layer to a non-woven fabric layer to form an outside layer, wherein the channel inserts have a cross section which matches the cross-sectional profile of each of the elongated channels of the panel. Structural foam is attached to the non-woven fabric layer of each of the panel and the plurality of structural foam channel inserts, wherein the structural foam fills interstices of the non-woven fabric layer without penetrating into the reinforcing fabric layer. The plurality of structural foam inserts are mated with the elongated channels of the panel after being saturated with curable resin after the structural foam has been attached to the non-woven fabric layer of each of the channel inserts and of the panel.